The invention relates to gas-tight sintered translucent aluminium oxide having a density of at least 99.5% and containing MgO in a quantity of at most 1000 ppm by weight. The invention further relates to a method of manufacturing an article from this material. Such a material is known from U.S. Pat. No. 3,905,845. The known material is gas-tight, is highly translucent and is widely used inter alia in discharge vessels of high-pressure discharge lamps. Besides MgO, Y.sub.2 O.sub.3 and La.sub.2 O.sub.3 are added in order to obtain a satisfactory density and a regular crystal size distribution of the sintered material. However, the addition of Y.sub.2 O.sub.3 and La.sub.2 O.sub.3 can give rise to .beta. aluminate crystal structures, which adversely affect the durability of the material. Especially in the case of the use as a wall of a discharge vessel in which sodium is incorporated, it is found that the .beta. aluminate structure can be very readily attacked by the Na.
The invention has for its object to provide a measure for obtaining gas-tight sintered translucent aluminium oxide having a regular crystal size distribution and being free from .beta. aluminate structure.